Blood thinners, such as warfarin, prevent blood clots from forming, thereby reducing the risk of a stroke or heart attack. When people undergo surgery or certain procedures, they must stop using warfarin to prevent too much bleeding during and after the surgery or procedure. Some doctors prescribe a different blood thinner, one that works more quickly and wears off more quickly, to bridge the gap between starting and stopping warfarin. However, this short-term treatment is expensive, may increase the risk of bleeding, and has not been proven effective. This study will determine whether a bridging blood thinner called dalteparin is helpful or harmful for people with atrial fibrillation who stop taking warfarin in preparation for surgery or a procedure.

Number of Arterial Thromboembolic Events [ Time Frame: from subject signing of the consent until completed the study (Day -30 to Day +37) ] [ Designated as safety issue: Yes ]

The events are defined as arterial thromboembolism: stokes, transient ischemic attack and systemic embolism events were independently and blindly adjudicated

Major Bleeding [ Time Frame: from subject signing of the consent until completed the study (Day -30 to Day +37) ] [ Designated as safety issue: Yes ]

Major bleeding is defined as symptomatic bleeding associated with transfusion of more than two units of packed red blood cells or whole blood, or death

Secondary Outcome Measures:

Number of Subjects With Death, Acute Myocardial Infarction, Deep Vein Thrombosis, or Pulmonary Embolism [ Time Frame: from subject signing of the consent until completed the study (Day -30 to Day +37) ] [ Designated as safety issue: Yes ]

Number of Participants With Minor Bleeding [ Time Frame: from subject signing of the consent until completed the study (Day -30 to Day +37) ] [ Designated as safety issue: Yes ]

Minor bleeding is defined as symptomatic or clinically-overt bleeding that does not satisfy the criteria for major bleeding

Approximately 2 million people in North America take the anticoagulant warfarin to prevent stroke, heart attack, and other events related to blood clots. Warfarin needs to be stopped before a person undergoes surgery or certain procedures because it can cause dangerous amounts of bleeding during and after surgery. Some doctors give a low molecular weight heparin (LMWH) to patients during the 2-week period when participants are without the effects of warfarin. The LMWH has the same effect as warfarin, but it acts and then leaves the system more quickly than warfarin. However, the LMWH is expensive, may increase the risk of bleeding, and has not been proven effective. This study will determine the safety and efficacy of an LMWH in adults with atrial fibrillation who stop warfarin in preparation for surgery.

Participation in this study will last between 36 and 67 days. Participation will involve nine points of contact with researchers, at least two of which will be in-person visits at the research clinic. The others will be conducted by phone. All points of contact will include assessments on possible bleeding and any new symptoms. The first two of these points of contact, will take place at the signing of the informed consent, which will involve a screening of medical records and random assignment of participants to receive either the LMWH dalteparin or placebo. Participants will self-administer a subcutaneous injection of their assigned treatment twice a day for 3 days before the surgery or procedure and for 6 days after. During the course of the study, when participants visit their primary physicians for regularly scheduled appointments, it will be recommended that they undergo two international normalized ratio (INR) tests of blood clotting ability between day 2 and 10 after the surgery or procedure. The remaining seven points of contact will occur sometime between the day before surgery and 37 days after surgery. One of the in-person visits will occur within the first week after surgery and will include assessments on possible bleeding, any new symptoms, and INR results.

Eligibility

Ages Eligible for Study:

18 Years and older (Adult, Senior)

Genders Eligible for Study:

Both

Accepts Healthy Volunteers:

Yes

Criteria

Inclusion Criteria:

Receiving warfarin therapy for at least 3 months, administered to achieve an international normalized ratio (INR) range of 2.0 to 3.0

Neurosurgery that is intracranial or intraspinal, such as tumor resection or aneurysm repair

High-risk non-surgical procedures, such as brain biopsy

Other surgical or non-surgical procedure that, at the discretion of the surgeon, precludes administration of therapeutic-dose low molecular weight heparin (LMWH) at any time in the post-procedure period

More than one surgery planned during the trial period

Prior participation in this trial

Contacts and Locations

Choosing to participate in a study is an important personal decision. Talk with your doctor and family members or friends about deciding to join a study.
To learn more about this study, you or your doctor may contact the study research staff using the Contacts provided below.
For general information, see Learn About Clinical Studies.

Please refer to this study by its ClinicalTrials.gov identifier: NCT00786474